The present invention relates to a new and improved construction of a roller apron or strand guide assembly -- sometimes also referred to in the art as a roller apron framework -- for a continuous casting installation, especially for casting steel, which particularly is of the type equipped with driving and/or straightening rollers, and in the direction of travel of the strand directly following roller pairs can be mutually displaced independently along comb-like arranged guides disposed to both sides of the machine frame transversely with respect to the direction of strand travel.
During the continuous casting of slabs and large bloom installations the strand is only partially solidified in the roller apron of the secondary cooling zone and oftentimes also upon entry into the driving- and/or straightening roller framework of curved- or arc-type casting installations. Such roller aprons are assigned the function of guiding the strand, supporting the ferrostatic pressure of the liquid core acting upon the strand shell or skin in order to prevent bowing-out, and introducing the dummy bar which is usually thinner than the strand thickness to be cast into the mold. Upon increase of the casting speed, in the case of arc-type continuous casting installations, the liquid core oftentimes extends for a considerable extent into the horizontally arranged portion of the roller apron and the driving machine or assembly, thus requiring long supporting roller aprons or supporting frameworks.
From U.S. Pat. No. 3,722,576 there is known to the art a withdrawal and straightening machine, the rollers of which are mounted independently of one another in the machine frame. Driven upper rollers of roller pairs are arranged upon transverse supports. The end surfaces of the roller bearings are provided with guides which are displaceable transversely with respect to the direction of travel of the strand in grooves of the machine frame. The non-driven lower rollers, situated opposite the driven rollers, are fixedly mounted in the machine frame. The roller pairs neighboring the roller pairs having driven rollers are likewise fixedly mounted at the machine frame. Such fixedly mounted rollers cannot positionally shift or deviate in the presence of overloads, such as for instance during straightening a strand which is too cold or during throughpassage of a bowed-out solidified strand. The consequence of such is roller rupture, bent rollers and damage to the bearings of the rollers.
U.S. Pat. No. 3,963,069 discloses a further prior art roller apron or roller apron framework for support- and drive rollers wherein two rollers which follow one another along a roller apron path are arranged upon a common, pivotable transverse support. At both sides of the rollers there are mounted at the roller bearings sliding blocks which are movable in guides provided transverse to the guided strand surface. The hingedly connected sliding block enables the transverse support to carry out a pivotal movement. For each of both rollers there is mounted at the transverse support an impact or stop surface which cooperates with support surfaces provided at the machine frame. In the presence of overloading of a roller the transverse support can tilt about one of the stop surfaces. The arrangement of, in each instance, two rollers upon a transverse support requires for exchange or replacement of the rollers relatively expensive and heavy roller changing units. Furthermore, the structure of the machine frame hinders exchange of the rollers of the lower roller track or path together with the associated transverse support. During disassembly of such lower rollers their bearings within the machine must be detached from the transverse support and upon assembly again connected, requiring long change times and reducing the availability of the machine.
British Pat. No. 1,241,918 discloses a roller apron for continuous casting installations having a partially curved strand guide arrangement or roller apron wherein in order to obtain short change times of the rollers, directly following or successive roller pairs are mutually displaceable independently of one another along guides arranged transverse to the direction of travel of the strand. These guides arranged at both sides of the machine frame between the rollers are of comb-like construction. The bearing of a roller pair slides along these guides, during the roller-exchange operation. During the casting operation the rollers which are hingedly connected at a transverse support are safeguarded against overload at the detachment side. For this purpose the transverse support is provided with two pressure cylinder means. The roller bearings or supports thus slide along the guide. At the fixed side, the roller bearings are rigidly attached to the machine frame. Between both rollers of a roller pair there are provided exchangeable intermediate elements which are accommodated to the strand format or shape. The rollers at the detachable side are capable of being brought into contact with such intermediate elements by the pressure cylinder means. With this roller apron the rollers are not protected against overload at the fixed side. Moreover, due to the sliding mounting of the roller bearings at the comb-like guide there is present a relatively large roller spacing or pitch and/or a weak dimensioning of these comb-like guides, which can lead to deformation of the guide and to an inexact roller apron geometry. Large roller spacing can lead to bowing-out of the strand and the attendant metallurgical drawbacks. By virtue of the pressure cylinder means arranged in the horizontal part of the guide above the roller apron, such roller apron construction, when using oil as the hydraulic fluid medium, also is prone to a latent danger of fires breaking out. Furthermore, at the fixed side, with this arrangement, it is not possible to employ any rollers having a number of roller bearings. When disassembling the rollers it is always necessary to also disassemble the pressure cylinder means.